Telephone system



w. G. SHULL TELEPHONE SYSTEM Filed Jan. 29. L921 Patented July 29, 1924.

OFFICE.

TELEPHONE SYSTEM.

Application filed January 29, 1921.

To all whom it may concern:

Be it known that I, WILLIAM G. SHULL, a citizen of the United States of America, and a resident of Chicago, county of Cook, and State of Illinois, have invented certain new and useful Improvements in Telephone.

Systems, of which thefollowing is a specification. 7

My invention relates to telephone systems 19 in which manual link or cord circuits are I provided for interconnecting telephone lines,

and has to do more particularly with the so-called multiple line lamp systems in which instantaneous disconnect and recall are provided. 7

In cord circuits of the above character provisions havebeen made whereby when a calling subscriber replaces his receiver upon the switchhook, means are provided in the 20 cord circuit. which, operate to disassociate the line current from the connected cord; Should the calling subscriber wish to recall after replacing his receiver upon the switchhook, the TGIHOVEtl OI the said receiver from its switchhook causes the multiple line lamps to again be lighted so that the recall may be seized by the same operator who handled the original connection, ,or by another operator, either one to the exclusion of the othen S3 A feature of my invention is the provision of means in the cord circuit whereby the line circuit of the called subscriber is disassociated from the connected cord circuit when he places his receiver upon the switchhook so that in case he wishes to recall the subsequent removal of the receiver will again bring about the lighting of the multiple line signals associated with his line so that the recall maybe seized by another operator.

Another feature of my invention is the provision of means whereby the called subscriber is prevented from initiatinga recall until after the calling subscriber has replaced his receiver, and the said means also prevents a calling subscriber from initiating a recall until after the called subscriber has replaced his receiver so that both subscribers must replace theirreceivers upon their respective switchhooks before their associated line circuits are disassociated from the con- Serial No. 440,854.

be more fully hereinafter described in the following specification.

For a better understanding of my inven- WILLIAM G. SHULL, OF CHICAGO, ILLINOIS, ASSIGNOE 'IO KELLOGG SWITCHBOARD AND SUPPLY COMPANY. OF CHICAGO, ILLINOIS, A CORPORATION 0F ILLINOIS.

tion, reference may be had to the accompanying drawing, in which I illustrate my invention operating in connection with a suitable telephone system.

In the drawing I show a calling substation A and a called substation D, the said calling and called substation A and D connected, respectively, at the exchange to line circuits L and L. The line circuits L and L at the exchange comprise, respectively, the usual line relays LR and LR, cut-off relays'CO and CO, multiple jacks J and J, and the multiple line signals S and S. The jacks of the lines are distributed among differen'toperators positions, and there is a line signal S for each jack so that when a call is initiated over any line, the line signals at the various operators positions are lighted, and any one of a plurality of operators may seize the call to the exclusion of the other operators.

The cord circuit C for interconnecting substations as A and D is provided with an answering plug AP and a calling plug UP, the said answering and calling plugs AP and CP being connected. by the heavily marked conductors. The answering end of the cord-circuit C is provided with a combined sleeve and link disconnect relay LD which is energized when the answering'plug AP is inserted into the ack J of the calling line. The relay LD is provided with a high resistance winding and a low resistance winding, and upon'the actuation of the said relay the hi gh resistance winding is shunted, and this prevents the relay LD in another cord from being energized should another operator attempt to answer the call after it has been seized by an operator, so that an operator at any other cord attempting to seize the call after the first operator has connected to the calling line is prevented from communicating with the subscriber; as

the shunt of the low winding of the relay LD of the first cord prevents the relay LD of the second cord from operating. As the said second operator is not connected to the relay AS to connect the operator's set 0 to a the cord conductors.

i The c-alling end of the cord circuit C- is provided with a combined sleeve and link disconnect relay LD', a'tuated when the calling plugGP is inserted 'ito the jack J of the called line. This relay upon energization opens the circuit of thelistening relay LS, which relay de-energizes to disconnect the operators set Q from the cord conductors. A party-line ringing key El: is provided for connecting any one of a plurality of generators G, G, G and G depending upon the key plunger that is depressed. to signal the called-for subscriber. An interrupter relay IR is energized upon the act-uation of the ringing key BK, the said relay remaining energized as long as the partyline ringing key RK is held in its fully depressed position to assure giving the called subscriber an instantaneous first ring. The

depression of the ringing key RK and the operation of relay Ll) closes a circuit for the ringing control relay RC, which relay RC controls the connection of ringing current to the called line, and also connects the interrupter I to the interrupter relay IE to intermittently energize and de-energize the said relay IR. A calling supervisory relay GS is also provided which is actuated upon the response of the called subscriber to interrupt the circuit of the relay BC to dis connect ringing current from the line of the answering called subscriber. A calling supervisory lamp CL is provided and is for the usual supervisory purposes. I provide ,5 a disc'onnect control relay DCE which relay is energized only after both substribers have replaced their receivers upon their respective switchhooks to condition the line circuits ot'th'e respective calling and called I line for arecalh as will be more fully hereinafter described.

Having described in general the arrangement of the circuits and apparatus employed iii my invention I will now describe in dei tail the operation of the apparatus in extending a call from the subscriber at thesubstation A to the subscriber at the called substation D.

Assuming now that the subscriber at the calling substation A initiates a call, the removal of the receiver at the substation closes an energizing circuit for the line relay LR- of the line circuit L from battery through the winding of relay LR, normal contact 2 of cut-ofl relay GO, through the substation A and back to ground at normal contact 3 of relay CO. The line relay LR upon energization closes its alt rnate contact 4 to light the line lamps S at a plurality of operators positions. Assuming that it is the operator associated with the cord circuit C that answers the call, the insertion of the answering plug AP into the jack J of the calling line establishes a series energizing circuit for the cut-off relay C0 of the line circuit L and the combined sleeve and link disconnect relay LD ot the cord circuit C, traced from battery through the windings 5 and 6 of the relay LD, conductor 'fiiiormal contact 8 of the disconnect control relay DCRQ conductor 9, sleeve contacts of the connected plug AP and aclt J and through the winding of the cut-off relay CO to ground. The closure ot alternate contact 10 of relay LD upon its energization closes a low resistance circuit through its winding 5 by shunting the high winding 6, this circuit being traced from battery through the low resistance winding 5, alternate contact 10 conductor 7, normal contact 8 of relay DCR, conductor 9, sleeve contacts of the connected plug AP and jack J to ground through the winding of cut-off relay CO. The high resistance winding 6 of the relay Ll) is shunted, this arrangement providing for secret service, as a relay LD of a second cord circuit will not operate in series with the cut-off relay CO as the shunt of the low resistance winding 5 of the relay LD of the first cord circuit renders the relay LD of the second cord circuit that attempted to answer the call inoperative.

The closure of alternate contacts 11 and 12 of the relay LD establishes an energizing circuit for the answering supervisory relay AS, traced from battery through the lower winding of relay AS, conductor 13, alternate contact 12 of relay LD, ring contacts of the connected plug AP and jack J, through the closed contacts at the substation switchhook, back through the tip contacts of the connected jack J and plug AP, alternate contact 11 or" the relay LD, conductor 1%, and through the upper winding of supervisory relay AS to ground, and the opening ofnormal contact 15 of the supervisory relay AS prevents the permature lighting of the answering supervisory lamp AL. The energizat-ion of the cut-off relay ()0 of the line circuit L opens the energizing circuit of the line relay LR, which relay restores and the interruption of its contact 4t etlaces the ate does not connect the operators set line singals S. The closing of alternate con- Y with the cord circuit C is connected thereto,

the low resistance path of the winding 5 of the relay LD prevents the relay LD of the second cord from operating, and the relay LD of the second cord circuit failing to 0 e1} 0 the second cord across the cord conductors. The second operator failing to receive a response when she answers, knows that the call has been answered by another operator 1 and withdraws the plug of her cord circuit from the multiple jack of'the calling line.

The operator having been connected to the cord conductors, now inquires the want of the calling subscriber at the substation A, and assuming that it is the subscriber at the substation D that iswanted, the operator now tests the multiple jack J of the called line asto its idle or busy condition, and if the line is, busythe operator will receive the usual busy click in the head receiver of her set.

Assuming that the line is idle, the operator inserts the calling plug -.CP into the multiple jack J of the called line D to close a series energizing circuit for the combined sleeve and link disconnect relay LD of the cord circuit C and the cut-oil relay C0 of the line circuit L associated with the called line D, the circuit being traced from battery through the winding of the relay LD', conductor 22, normal contact 23 of the disconnect control relay DCR, conductor 24, sleeve cont-acts of the connected plug CP and jack J and through the winding of the cut-oil relay CO to ground. The 0 ening of normal contact 19 of the relay ,D opens the energizing circuit of the listening relay LS, and the said relay LS restoring opens its alternate contacts 20 and 21, to disconnect the operators set C from the cord conductors.r

The closing of alternate contact 19 of the relay LDt establishes a circuitfor the call-- ing supervisory-lamp CL, traced from battery through the calling supervisory lamp CL, normal contact 2501f the ringing control relay RC, conductors 26 and 27, normal contact 28 of thecallingsupervisory relay CS, conductors 29 and 30 to ground at alternate contact 19 of the relay LD, and the" said calling 'supervisorylamp CL is lighted over this circuit and remains lighted until the operator depresses the party-line ringing key RK. The operator having inserted the plug CP now depresses the proper ringing key plunger of the party-line ringing key RK to its fully depressed position to close the end spring contacts 31 and 32 and to connect the proper ringing generator G, Gr, G or Gr to signal the called-for subscriber at the substation D. The closing of alternate contact 32 of the end springs of the party-line ringing key RK brings about the energization of the ringing control relay, RC during the interval that the key RK is held down, over a circuit traced from battery throu h the winding of the ringing control relay i tC, conductor 33, closed end spring contact 32, conductors 34 and 35, normal contact 36 of the disconnect control relay DCR, conductor 27, normal contact 28 of calling supervisory relay CS, conductor 29 and 30 to ground at alternate contact 19 of relay LD. The closing of end spring contact 31 brings about the energization of the interrupter relay IR during the interval that the ringing key RK is helddown, over a circuit traced from battery through the upper winding of relay IR, conductor 37,

energized, due to the closure of the end.

spring contact 32, as already described, closes its alternate contact 41 to establish a locking circuit for itself traced from battery through the winding of ringingcontrol relay RC, its alternate contact 41, conductors 34 and 35, normal contact 36 of relay DCR, conductor 27, normal contact 28 of relay CS, conductors 29 and 30 to ground at alternate contact 19 of the relay LD. The openingof normal contact 25 of the relay RC now effaces the callingsupervisory signal CL. g i I The closing of alternate contact 42 of relay RC connects interrupter I to the lower winding of the interrupter relay IR, the circuit being traced from ground, through the constantly rotating interrupter I, alternate contact 42 of relay'RC, conductor 43 to battery and ground through the lower winding of interrupter relayQIR. The relay IR is intermittently energized and de-energ'ize'd over this circuit toconnect ringing generator G to the called line' over-a circuit traced from the tin-grounded pole of the generator G, alternate contact 44 of the depressed ringingkey plunger, conductor 45, alternate contact 40 of relay IR, tip contacts of the connected plug CP and jack. J, through the condenser and call bell at the called substation D, back through the ring contacts of the connected jack J and plug GP, to ground through alternate contact 46 of relay IR.

The closing of alternate contact 47 of the interrupter relay IR transmits a ringing tone to the calling subscriber at the substation A, the ringing tone being traced from the low frequency generator G which is of 16 cycles, over conductor 48, through resistance 49, condenser 50, alternate. contact 47 of relay IR, conductor 51, alternate contact 52 of relay LD, alternate contact 11 of relay LD, tip contacts of the connected plug AP and jack J, through the receiver at the calling substation A, back through ring contacts of the connected plug AP and jack J, alternate contact 12 of relay LD, conductor 13 and through the winding of the answering supervisory relay AS to battery and ground. This tone just traced gives the calling subscriber at the substation A an audible signal notifying him that the called subscriber at substation D is being signaled. The called subscriber at the substation D is thus automatically signaled until he answers in response to his call signal, or until thecalling subscriber replaces his receiver before the called subscriber answers.

Should the calling subscriber at the substation A replace his receiver before the called subscriber answers, the answering supervisory relay AS will restore, due to the open switchhook contacts at the calling substation A.. The closing of normal contact 15 of the answering supervisory relay estab-. lishes an energizing circuit for the disconnect control relay DCR tracedfrom battery through the winding of said relay DCR, conductor 53, normal contact 54 of the calling supervisory relayCS, conductor 55, normal contact 15 of answering supervisory relay AS, conductor 56, alternate contact 57 of the relay LD, conductor 30 to ground at alternate contact 19 of the relay LD. The disconnect control relay DCR upon energization opens its normal contact 36 which opens the locking circuit of the ringing controlrelay RC, which relay now de-energizes and restores, and the opening of its alternate contact 42 disconnects. the. interrupter .I from the interrupter relay IR. The relay IR rest-ores. to normal, opening its alternate contact 40. to prevent further application of ringing current to the called line. The relay DCR upon energization opens its normal contacts 8 and 23 to open the energizing circuits of the combined sleeve. and link diseanee s elay L and 1 D r. r rest y and the said relays LD and LD' now restore, opening the initial energizing circuit of the disconnect control relay DCR. at their re? spective contacts 57 and 19, but due to the slow to release construction of the relay. DCR it is momentarily held energized until a locking circuit is established for it which may now be traced from. battery through the winding. of relay DCR, its alternate contact 60, conductor 61, normal contact 62 of-relay. 63, conductor 64, normal contact of relay LD, normal contact 40 of relay IR, tip con tacts of the connected. plug. CP and jack J to ground at normal contact 3 of the outoif relay C0 of line circuit L, the said out off relay CO having restored to normal, upon the energization of relay DCR, which relay interrupted the series energizing cir-- cuit of the relay LD' and the cut-off relay CO at its normal contact 23. The closing of alternate contact 36 of relay DCR establishes a circuit for the calling supervisory lamp CL, traced from battery through the lamp CL, normal contact- 25 of relay RC, conductors 26 and 27 to ground at alternate contact 36 of relay DCR, bringing about the lighting of the calling'supervisory signal CL. A circuit is also established for the answering supervisory lamp AL, traced from battery through the lamp AL, conductor 55, normal contact 54 of relay CS, conductor 53, alternate contact 60 of relay DCR, conductor 61, normal contact 62 of relay 63, conductor 64, normal contact 65 of relay LD', normal contact 40 of relay IR, tip contacts of the connected plug CP and jack J to ground at normal contact 3 of relay CO, the said answering supervisory lamp AL being lighted over this circuit. The answering supervisory lamp AL and the calling supervisory lamp CL are now lighted over the above traced circuits and indicate to the operator that disconnection 'is desired, which now takes place in the usual manner. i i i Assuming that the subscriber at the called substation D, in response to his callbell removes his receiver from its switch-hook, when the interrupter relay IR is in one of its de-energized positions, an energizing circuit is established for the calling supervisor relay CS, traced from battery through the lower winding of relay CS, conductor 70, alternate contact 71 of relay LD, normal contact 46 of relay IR, ring contacts of the connected plug CP and ack J, through the now closed contacts of the substation switchhook, back through the tip contacts of the connected plug CP and jack J, normal contact 40 of relay IR, alternate" colitact 65 of relay LD, conductor 7 2 and through the upper winding of relay CS to ground. The opening of normal contact 28 of relay CS opens the locking circuit of the ringing control relay RC, which relay de ener izes to open its alternate contact 42, whici disconnects the ringing interrupter I from the lower winding of the relay IR. The relay IR nowremains at normal and the opening of its alternate contact 40 prevents further application of ringing current to the called subscribers line.

The calling and called subscribers at the substations A and D are now in conversation, the talking circuit being traced over the heavily marked conductors. After the subscribers have finished conversation, they replace their receiversupon their respective switchhooks, causing the answering and calling supervisory relays AS and OS to restore due to the opening of the switchhook contacts at the respective substations A and D. The closing of normal contacts 15 and 54 ofthe respective supervisory relays AS and CS closes an energizing circuit for the disconnect control relay DCR traced from battery through the winding of relay DCR,

conductor 53, normal contact 54 of the calling supervisory relays CS, conductor 55, normalcontact 15 of answering supervisory relay AS, conductor 56, alternate contact 57 of the relay LD, conductor 30 to ground at alternate contact 19 of the relay LD. The relay DGR upon energization opens its normal contacts 8 and 23 and the opening of normal contact 8 interrupts the energizing circuit of the relay LD, and the opening of normal contact 23 opens the energizing circuit of the relay LD and the two relays LD and LD now restore to normal. The relays LD and LD open their respective contacts 57 and 19, opening the initial energizing circuit oi the disconnect control relay DCR, but'dueto the slow-t0- release construction of the relay DCR, it is momentarily held energized until a locking circuit is established for it, which may now be traced from battery through the winding of relay DCR, its alternate contact 60, con- 7 ductor 61, normal contact 62 of relay 63, conductor 64, normal contact 65 of relay LD, normal contact 40 of relay IR, tip con tacts ol the connected plug GP and jack J to ground at normal contact 3 of cut-off relay CO, the said relay CO having restored when the series energizing circuit of the relay LD and CO was interrupted at contact 23 upon the energization of relay DCR. The series energizing circuit of the relay LD and cut-oii' relay CO is interrupted at the contact 8 of the energized relay DCR and relays LD and CO restore. The relay LD upon restoration opens its alternate contacts 11 and 12, disassoeiating the calling line from the strands of the link or cord circuit C, and the restoration of relay LD opens its alternate contacts 52 and 71, disassociating the called line from the strands of the cord circuit C. The closing of alternate contact 36 of the relay DCR establishes a circuit for the calling supervisory lamp CL, traced from battery through the lamp CL, normal contact 25'0f relay RG, conductors 26 and 27 to ground at alternate contact 36 of relay DOB, and the lamp CL is thus lighted over this circuit. A circuit is also established for the answering supervisory lamp AL traced from"battery through the lamp AL, conductor 55, normal contact 54 of relay CS, conductor 53, alternate contact 60 of relay DCR, conductorfil, normal contact 62 of relay 63, conductor 64, normal contact 65 of relay LD, normal contact 40 'ofrelay IR, tip contacts of the connected plug GP and ack J to ground at normal contact 3 of the relay CO, and the answering supervisory lamp AL is thus lighted over this circuit. The closing of alternatecontact 23 of relay DCR connects relay 63 over conductor 24 to the sleeve of the connected jack J, but relay 63 is not energized at this time as ground from the sleeve of the connected jack J extends over the sleeve contacts of the jack J and plug CP over conductors 24 and through alternate contact 23 of relay DCR to one terminal of the winding of relay 63, while the other terminal ofthe winding of relay 63 is also connected to ground. The ground potential upon the sleeve of the multiple jacks J prevents the sleeves of the jacks J from testing busy when the subscribers have replaced their receivers and the plugs AP and GP are still connected in the respective jacks J and J so that, should another operator test the line of substation D as to its idle or busy condition, the opera tor in testing a multiple jack J will not receive a busy click even though the plug CP is still in the jack J. Thus, should an operator be busy handling other connections and permit the plugs AP and GP to remain in the jacks, the lines are immediately available as called lines and will test idle.

The operator noting the two lighted supervisory signals AL and CL removes the answering plug AP and calling plug GP from their respective jacks J and J, and the remo al of the calling plug GP from the jack J of the called line opens the energizing circuit of the disconnect control relay at the tip contacts of the plug GP and jack J, and the relay DCR upon de-energization opens its alternate contacts 60 and 36, which opens the circuits of the answering and calling supervisory signals AL and CL, respectively, thus efiacing the two signals. The removal of the plug AP from the jack J of the calling line disconnects the answering end of the cord circuit C from the calling line, and the apparatus used in establishing a connection-between the calling subscriber at substation A and the called subscriber at substation D is now at normal and available for establishing other connections.

Assuming now that the subscribers at the relay L'R of prevent a second "may now be seized by'the operator who han filed the initial connection, or by an operator at another position.

Assuming Lthattheoperator who origifnally established the connection seizes the recall, the said operatorassociated with the cord circuit C withdraws the calling plug fCP'trom'the jack J of the called line. This withdrawal of the "plug GP opens the lock- ".in g circuit of the disconnect control relay DOB at the tiprcontacts of the now disconnected plug GP and jack J, and the irelay;1DCR now restores. The closing of 'normalcontact 8 of the restored relay DOB again closes an energizing circuit for the :combined. sleeve "and link disconnect relay IJ'Dironi battery through windings 5 and 6 0f the relay LD 'to-.;ground through the winding ofithe cut-oft relay CO, as pre- *viously described. The closing of alternate contact "10 of relay LD establishes a circuit lthrough "the ilow resistance winding 5 of relay LD, which shunts the high resistance winding 6 of the said relay LD to i l V operator from seizing the recallQas alreadydescribed. The closing of alternate contacts 11 and 12 of relay LD establishes a circuit for the calling supervisory relay AS, as previously described, and the closing of alternate contact 16 of relay 'AS closes an energizing circuit for the listening 'relay LS as already described, and the closing of alternate contacts 20 and A 21 of the listening relay LS connects the she now inquires the wants of the operator-7s set 0 to the cord conductors, and recalling subscriber at substation A. The operator now tests the line wanted by the recalling subscriber in the usual manner, and the connection fromthis point is the same as pre- 'viously described, and a further description is not necessary.

Should an operator other than the one associated with the cord circuit C answer the recall before the operator of the cord circuit C can'seize it, the low resistance path through the winding of the relay LD of the second cord that is connected to the recalling line A .prevents the relay LD of the "cord circuitflC from operating for the reasons already described, and the operator at the cord ClICUlt G failing to recelve a response knows that the call has been anceiver at the substation D closes an energizing circuit for the line relay LR,

through the switchhook contacts, and the closing of alternate contact 4 of relay LB j brings about. the lighting of the multiple line signals S. The line signals appear before a plurality of operators as previously described, and any one of the operators before whom the signals S appear may seize the recall to the exclusion of the others. The operator seizing the recall inserts the answering plug AP of a cord pair into the multiple jack J of the recalling line D, thereby establishing a series of 'energizing circuit for the combined sleeve and link disconnect relay LD of the cord used andthe cut-off relay C0 of the recall ing line D. The operation of the recalling connection from this point is the same as pre-.

viously described, and a further description is not thought necessary. The operator of the cord circuit C that supervised the original connection between the substation Aand the now recalling substation D cannot seize. 0

the recall of the called substation, while either plugs AP or OP remain in the jacks J and J, but the operator may withdraw both theanswering and calling plugsAP and GP from the acks J and J, and then establish a connection with the recalling line D by inserting the answering plug AP into'the jack J 01 therecalling line and handle the call in the usual way, as previously described. 7 i

The insert-ion of the plug AP ofthe cord seizing the recall of substation D. places a busy or battery potential upon the sleeves of the multiple jacks l of the recalling line for the usual busying purposes, and this battery also extends from the sleeve of the jack J with which the calling plug GP of the first cord circuit is still connected to the sleeve of the plug GP, over conductor 24,

through alternate contact 23 of relay DCR.

and through the winding of relay 6?), to ground. The locking circuit of relay DCR was interrupted upon the energization of'the cut-o trelay CO when the recall was seized by another operator, as before described, by, the openingot normal contact 3. The relay DCR being slow to release is held momentarily energized. unt l a substitute locking circuit is established for it, upon the energization of the relay 63, as above described,

which upon energization closes its alternate contact 62, establishing this substitute circuit traced from battery through the winding of relay DCR, its alternate contact 60, conductor 61, to ground at alternate contact 62 of relay 63. The relay 63 and relay DCR will remain energized until the operator of the cord circuit C withdraws the plug GP so that there will be no possible interference with the recalling line, as is readily apparent. When the operator of cord C withdraws the plug CP from the jack J, relay 63 restores and the opening of its alternate contact 62 opens the locking circuit of relay DCR, which now restores to normal and the withdrawal of the plug AP from the jack J now restores the apparatus of cord circuit C to normal and it is available for use in establishing other connections.

From the above description it may be seen that both receivers of the respective parties must be upon their respective switchhooks before a recall by either party may be initiated. Should the called subscriber at the the disconnect control relay DGR, so the link disconnect relays LD and LD remain energized through the normal con- .tacts 8 and 23 of relay DCR. Now, when the subscriber at substation A removes his receiver to recall, this removal of thereceiver will again energize supervisory relay AS and again eflace the supervisory signal AL. The link disconnect relays LD and LD are held energized in series relation with cut-off relays CO and CO, respectively, and the line circuit L of the calling substation A is not disassociated from the cord circuit C,

and the cut-off relay CO remaining energize-d, the line signals S are not lighted. Thus, it will be seen that all the recalling subscriber can do is to wink his switchhook to flash the supervisory signal AL. Shouldthe calling subscriber at substation A fail to replace his receiver and should the called I subscriber replace his receiver and then mmediately recall, this action of the cord circuit C would be the same in that relay DCR- would fail to energize due to the continued energizationof the answering supervisory relay AS and thus the subscriber at substation D under these conditions will only control the calling supervisory lamp What I claim as new and desire to. secure 2 by Letters Patent, is

1. A telephone system including a pair of telephone lines connected for conversation by means of link circuit applied to mulv tiple terminals of said lines, means controlled by the subscribers jointly to operatively free both lines from sa1d link circuit while applied to said terminals, sald means including a pair of relays one for each line energized during conversation, each to close a switch contact in the talking circuit between said lines. y

2. A telephone system including a pair of telephone lines, a link circuit for interconnecting said telephone lines in conversational circuit, normally open contacts in the talking conductors of each end of said link circuit, a pair of relays energizable to close said contacts during conversation, means Controlled by t Subscribers jointly to deenergize said relays to open said contacts to free said lines from said link circuit.

3. Atelephone system including a call" ing line and a called line, and a link circuit interconnecting them having a talking strand with a normally openswitch contact, a link circuit relay normally conductively connected between one pole of a source of current and a terminal of said link circuit and energized by the application of said terminal to the calling line, said relay serving on energization to close said switch contact, means controlled over the calling line and called line to de-energize said relay, multiple terminals for said line, and switching means controlled over a contact of said relay to remove a busy condition from said terminals while. said link circuit remains connected with said line.

l. A telephone system including a calling line and a called line interconnected for conversation by link circuit means applied to terminals of said lines, said means including a relay having one end of its winding normally connected to battery and the other end contacts closed when said relay is energized,

and means cooperatively cont-rolled over the calling and called line to free said lines from busy test and to recall while said link -circuit is: connected totermina-ls of-sa-i-dlines. f5. Atelephonesystem lncludmg a. call ng line and a l111k circuit applied" to'a' multiple terminal thereof, a relay for said link'fcircuit energized on such application to closetal'king contacts of said link c1rcn1t and to shortcircuit a portion of its winding, a ca'lledfline connected to said calling line oversaid link circuit, and switching means controlledover said lines to make them test idle and display'signals while said"link circuit is applied to said multiple terminal, said switching means including acontactof-said relay.

6. A telephone system includingate' lephone line prorided with multiple terminals, 1 link circuit connected to one of said terminals, a relay forsaid 'lin'k circuiten'ergized. on connection" to close a talkingcontact 01 said circuit,-means to establish alow resistance holding circuit for said relay, subscriber-operated apparatus to cause saidfline to test idlewhile said circuit is connected to said terminal, and means to display a recall signal before an operator.

'7. A telephone system inchidin'g' a telephone line providedwith multipleterminais,

a link circuit connected to one of said terminals, a relay for said link circuit'energized on connection, means to establish a low resistance holding circuit for said relay for secret service purposes, a second relay for said link circuit connected to said terminal and so to said telephone line 'by'the energizatlon of said first relayyand means responsive to said -second relay to 'd'e-ener- 1 vgiize the first, said means including a: third "8; A telephone system including a tele phone'line and a link circuit having 'a terminal connected to afmultiple terminal thereof, a link circuit relay'for operation-by current oversaid line normally disconnected "from said link circuitterminah'another relay connected in; series "with battery by the c'onnection ofsald c1'rcu1t and said lme and-energized to close atalkingcontact to connect said first relay to said line, means forceenergiz'ing "said other relay controlledby said first relay, and athird relay to remove "clear 'atthe cord andgthe'other-serving to remove the busy test from jthe li-ne,"a third J relay for saidlink circuit for'jcl'osin'g. anon-.- gt'a'ct of the' circuitofsaid otherrel ay fsaid first relay controlling contacts'in'the circuit esteem of-said t third relay, a {supervisory signal of holding said relay energized during 0011- 'vers'ation, J said relay provided with means for pretenting another cord circuit from being operatively connected to said line While "said relay is 'ei'iergized, means con- *trolledcver said line to de-energme said 'relay to switch the-subscribers line limbs free at "the cord byopening said strands,

and a relay energized by the subscriber to *free his line from busy potential.

IlgAftelephone systemfincluding a pair of telephone lines connected for conversation=by means of a link circuit applied 'to multiple terminals of said lines, means con "trolled by" the subscribers jointly to operatively free both lines from said link circuit while applied to said terminals, said means incl'i'i'c'ling a pairof relays one for each line "energized. during conversation, each to close 'aswitch contact in'the talking circuit be-" "tween said lines, supervisory signals forsaid uli'nfk circuit, line signals for said lines respectively, and means whereby the subscrib'ers cause thedisplay of saidwsupervis ory signals and-of their respective line signa-ls sil'nultan 'eously 12. A telephone system including a calling li ne fand a called line, and a link/circuit interconnectingthem having a talking strand with:anormallyopen switch contact, alink' circuit relay norm-ally conductively connected between one pole. of a source of curjr'en't'and' a terminal ofsaid link circuit and "energized by :the application of said ter- 'lninaljto"thecalling line, said relay serving 'on energization to close said switch contact,

'means controlled over the calling line and calledgline "to de-energize said relay, multipleter-minalszior said line, and switching means'controlled over a contact of said relay to :remove a busy condition from said termin'als while said link circuit remains connected with said line, line signals for the calling and called, line respectively, and means for-displaying said signals while said 'lii k circuit"remains applied to terminals of said lines.

"-Signed by Fme'at-Chicago, in theecounty of-Cookand Stateof Illinois, this 27 day of January, 1921.

WILLIAM G. SHULL.

contacts of acord circuit r'elay, meansfor 

